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Spectroscopy

Structural Analysis

(Application of Woodward-Fieser Rules)

U.A. Deokate

Copyright by U. A. Deokate, all rights reserved.

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Woodward-Fieser Rules

It is used for finding absorption maxima

position (Max)

This differs from observed values by 5-6%.

Effect of substituent groups can be reliably

quantified by use Woodward Fieser Rule

Separate values for conjugated dienesand trines and --unsaturated ketnones

are available

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Woodward-Fieser Rules Woodward and the Fiesers performed extensive studies of

terpene and steroidal alkenes and noted similar substituentsand structural features would predictably lead to anempirical prediction of the wavelength for the lowest energyp p* electronic transition

This work was distilled by Scott in 1964 into an extensivetreatise on the Woodward-Fieser rules in combination withcomprehensive tables and examples (A.I. Scott,Interpretation of the Ultraviolet Spectra of Natural Products,Pergamon, NY, 1964)

A more modern interpretation was compiled by Rao in 1975 (C.N.R. Rao, Ultraviolet and Visible Spectroscopy, 3rdEd., Butterworths, London, 1975)

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Terminology

Alkenes are named by dropping the -ane endingof the parent and adding -ene.

Conjugated :organic compound; containing two

or more double bonds each separated from theother by a single bond

Dienes: One of a class of organic compoundscontaining two ethylenic linkages (carbon-to-

carbon double bonds) in the molecules. Alsoknown as alkadiene; diolefin.

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Terminology

Endocyclic double bonds have both

carbons in the ring and exocyclic double

bonds have only one carbon as part of the

ring.

Cyclopentene is an example of an endocyclic

double bond.

Methylenecylopentane is an example of anexocyclic double bond.

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Woodward

Fieser

Rulefor

Dienes

&

Polyenes

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Problem Illustration -1

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Problem Illustration -2

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Problem Illustration -3

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Problem Illustration -4

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Woodward

Fieser rule for

undsaturatedcarbonyl

compound

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Problem Illustration - 5

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Problem Illustration - 6

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Problem Illustration - 1

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Problem Illustration - 2

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Worked Problem - 1

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Worked Problem - 2

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Worked

Problem -

3

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Worked Problem - 4

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Worked Problem - 5

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Worked Problem - 6

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Worked Problem - 7

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Worked Problem - 8

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EMPIRICAL

RULES FOR

BENZOYL

DERIVATIV

ES

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Problem - 1

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Problem - 2

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Problem -3

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Problem -4

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Problem- 5

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Fieser Rules

If more than four double bonds are present the

Woodward rule is not applicable

The plant pigments contains double bonds up to

11 for this Fieser Rules is used. Max= 114 + 5(M) +n(48-1.7n)- 16.5Rendo-10 Rexo

n=no of conjugated double bonds

M= no of alkyl or alkyl like Substituents

Rendo= No of endocyclic double bonds

Rexo = No of exocyclic double bonds

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Fisher Problem-1

Max= 114 + 5(M) +n(48-1.7n)- 16.5Rendo-10 Rexo

= 114 + 5 (8) + 11(48-1.7x 11) 0 -0 = 476

Fisher formula

http://localhost/var/www/apps/conversion/tmp/studymaterail/fisherformaula.xlshttp://localhost/var/www/apps/conversion/tmp/studymaterail/fisherformaula.xls

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Fisher Problem-2

Max= 114 + 5(M) +n(48-1.7n)- 16.5Rendo-10 Rexo

= 114 + 5 (8) + 11(48-1.7x 11) 0 -0 = 476

Fisher formula

http://localhost/var/www/apps/conversion/tmp/studymaterail/fisherformaula.xlshttp://localhost/var/www/apps/conversion/tmp/studymaterail/fisherformaula.xls

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Fisher Problem-3

Max= 114 + 5(M) +n(48-1.7n)- 16.5Rendo-10 Rexo

= 114 + 5 (8) + 18(48-1.7x 18) 0 -0 =

Fisher formula

http://localhost/var/www/apps/conversion/tmp/studymaterail/fisherformaula.xlshttp://localhost/var/www/apps/conversion/tmp/studymaterail/fisherformaula.xls

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